The invention relates to a method of treating lumpy or granular materials with gaseous media.
Particulate materials, such as lime, magnesite and dolomite, are treated for various purposes in different ways such as heated, cooled, dried, smouldered, roasted, sintered, burnt or reduced. With these methods of treatment, a gaseous medium is guided through the granular material at a certain temperature and possibly under elevated pressure. The methods of treatment listed as examples differ from one another in temperature, pressure, demand or occurrence of heat, and duration of treatment.
For the treatment of granular materials with a gaseous medium, numerous methods have been known which use various arrangements. Thus, for instance, for treatment at high temperatures (up to approximately 1,500.degree. C.), such as in roasting, sintering, burning or reducing, shaft furnaces or retortes, revolving cylindrical furnaces, burning plants or a combination of these devices are used. All the methods of treatment which can be carried out with these arrangements, however, have the disadvantage that they are suitable for certain materials only.
A shaft furnace or a retorte, for instance, is not suited for sintering, since the sintered material cannot be carried out. Also a material which is not sufficiently gaspermeable because of its packing density cannot be treated by using these arrangements. Furthermore, it is difficult to subject the material to be treated to an intermediate treatment, and it is also difficult to control the treatment process.
When using a revolving cyclindrical furnace, the methods of treatment can be varied more easily, yet the costs of investing in such a furnace are very high. A further disadvantage consists in that it is uneconomical as regards its thermal efficiency. Process changes in wide ranges can be carried out with this furnace, but only over a long period of time.
Furthermore, it has been known to use travelling grates for treating granular materials. Such travelling grates are formed by grate cars joined together to form a continuous chain that continuously travels through a furnace. When the treatment temperatures are high, there is the danger that the grates will become overly deformed or even destroyed, since the treatment gases are also pressed or sucked through the grate. When the treatment temperatures are very high and the periods of treatment are very long at the same time, such as is necessary when calcinating limestone, travelling grates are not suitable. But, methods using travelling grates are also not suitable for types of treatment carried out at low temperatures, for which high pressure differences are necessary (e.g. for the drying of coal), since it is not possible to maintain high pressure differences.